An electrode assembly includes a plurality of unit cells, each including a positive electrode, a negative electrode, and a separator disposed therebetween, and a single separation sheet disposed between the unit cells while surrounding side surfaces thereof. First and second stack parts of unit cells are wound with the separation sheet from each end of the separation sheet toward the middle of the separation sheet, a facing unit cell has one surface that contacts the first stack part with the separation sheet between the one surface of the facing unit cell and the first stack part and the other surface that contacts the second stack part with the separation sheet between the other surface of the facing unit cell and the second stack part, and the unit cells are stacked such that electrodes having opposite polarities are disposed in contact with each other with the separation sheet therebetween.